Clutch and throttle cable and tools to replace them, an OLD set of plugs you know work. condenser. By the way, remove and oil clutch and throttle cables before and after winter and they will last a long time. The usual place they break, is at the clutch lever and throttle. Watch for any fraying.
Tools needed to adjust points (include feeler gauge) and take of points cover, tools to remove carby, carby float bowl and jets, headlight and tail light globeschain adjusting tools and spare chain link. Tools to adjust clutch (and get to it), tappet adjusting tools.

If you find that some nuts tend to loosen over time, carry the needed spanners for them.

Roll of electrical tape, roll of electrical wire, small head torch with good batteries (I always carry one and a spare set of batteries in my leather jacket). Octo straps and some baling twine and a few feet of packing wire.

On a longer trip take a spare rear tube (you can ususally find a tyre place on week days or sat morings, but they doften won't have m/cycle tubes), oil (if it's a bike only oil) and chain lube (I find Chain Wax to be the best).

I also carry a basic first aid kit...long stretch bandage (breaks and sprains), some sanitary pads (great for deep gashes) and a few large band aids.

If on a ride with someone else. chuck in a light rope 10' long in case someone needs to be towed.

I normally carry
spare pair of plugs (already mounted in the head on the opposite side)
Plug spanner
Allen key set
Shifter
pair of screwdrivers
leccy tape
various zip ties
couple of occy straps
small wire cutters (come in handy for fixing exhaust mounts with farm fence)
spare set of points